1. Field of the Invention
The present invention relates to a DC/DC converter circuit having a plurality of DC/DC converters and a battery system which includes a DC/DC converter circuit.
2. Description of Related Art
In future, both in stationary applications, for example, in wind power plants, and also in vehicles, for instance, in hybrid vehicles and in electric vehicles, increasingly new battery systems will be used which have to satisfy high requirements with respect to reliability. These high requirements are founded on the fact that a failure of the battery system is able to lead to a failure of the overall system (for example, in an electric vehicle, the failure of a traction battery leads to a disabled vehicle or even to a safety-relevant problem (in wind power systems, for instance, battery systems are used in order to protect the system from inadmissible operating states by rotor blade adjustment during strong winds).
It is known that one may convert the voltage provided by a battery to another voltage, using a DC/DC converter (also designated as a DC motor controller). The conversion of a constant input voltage, supplied by the battery, to a different output voltage usually takes place by periodic switching of the DC/DC converter. Boost converters, forward converters, half-bridge converters and full-bridge converters, for example, are known as common DC/DC converters.
FIG. 1 shows a known half-bridge converter 31. Known half-bridge converter 31 includes a primary circuit 42 and a secondary circuit 43.
Primary circuit 42 has a transformer coil 34a on the primary side, secondary circuit 43 has a transformer coil 34b on the secondary side, the primary side transformer coil 34a and the secondary side transformer coil 34b being connected to each other to form a transformer.
Primary circuit 42 includes an H-bridge circuit having a first branch running from a first node 36 to a second node 37, and a second branch and a bridge branch lying between the first branch and the second branch. Primary side transformer coil 34a is situated in the bridge branch. In the first branch there is a first switch 35a and a first capacitor 38a and in the second branch there is a second switch 35b and a second capacitor 38b. In parallel to first capacitor 38a there is a first resistor 44a, and in parallel to second capacitor 38b, a resistor 44b is connected. The first branch is connected to a ground 39. Furthermore, first primary circuit 42 has a first input 50a and a second input 50b, at which a battery 49 is connected.
Secondary circuit 43 includes a rectifier circuit 40 and a low-pass filter 41. Rectifier circuit 40 includes three diodes 45a, 45b, 45c, by the use of which the voltage generated by secondary side transformer coil 34b is rectified. The tapping of the voltage at secondary side transformer coil 34b takes place, in this instance using a midpoint tap. Low-pass filter 41 has a coil 46 and a capacitor 47. The voltage generated in secondary circuit 43 is able to be tapped at a first output 48a and at a second output 48b. 
The functional principle of half-bridge converter 1 shown in FIG. 1 is as follows: Battery 49 provides a voltage which charges capacitors 38a, 38b to one-half the battery voltage, via balanced resistors 44a, 44b. Switches 35a and 35b are now alternatingly opened and closed, so that, via primary side transformer coil 34a, an alternating voltage having an amplitude comes about that corresponds to one-half of the battery voltage. This alternating voltage is coupled into secondary circuit 43 using secondary side transformer coil 34b, and rectified via rectifier circuit 40. The rectified, pulse-shaped output voltage thus created corresponding to the pulse duty factor of switches 35a, 35b is smoothed via low-pass filter 41.